The present invention relates generally to non-aqueous batteries and specifically to lithium ion satellite batteries, and more particularly, to a charge control circuit for use with lithium ion satellite batteries.
Lithium ion batteries have unique characteristics that greatly impact charge/discharge control. Unlike nickel cadmium and nickel hydrogen cells, lithium ion cells cannot be over charged or discharged without irreversible damage. The key charge control issues for lithium ion batteries are the following.
The first issue is that each battery cell must have independent maximum over-voltage control during charging (typically at 4.1 V to 4.2 V depending on temperature, aging, etc.). The second issue is that battery cells should have independent undervoltage control during discharging (typically 3.0 V). The third issue is that there must be a means of bypassing a cell that has failed open or is demonstrating anomalous behavior. Furthermore, a fourth issues is that a modular, expandable, system is highly desirable and beneficial.
Commercial batteries generally only address the first issue and a variety of charge control methodologies have been proposed. However, with one exception these methods employ active bypass circuitry that generates substantial waste heat as current which is shunted past cells that have reached a full state of charge.
Accordingly, it is an objective of the present invention to provide for an improved charge control circuit for use with lithium ion satellite batteries that overcomes the limitations of conventional charge control circuits.